Protective system



TRENCHAM PROTECTIVE SYSTEM Filed Jan. 16, 1922 Inventor: Henry'T rencham,

Patented Oct. 21, 1924.

UNITED STATES PATENT OFFICE.

HENRY TRENCHAM, OF RUISLIP, ENGLAND, ASSIGNOR T GENERAL ELECTRIC COM- PANY, A CORPORATION OF NEW YORK.

PROTECTIVE SYSTEM.

Application filed January 16, 1922. Serial No. 529,482.

To all whom it may concern:

Be it known that I, HENRY TRENCHAM,

a subject of the King of Great Britain, re-

siding at Belsaye, Ruislip, county of Mid dlesex, England, have invented certain new and useful Improvements in Protective Systems, ofwhich the following is a specification.

My invention relates to improvements in protective systems and more particularly to systems of the pilot wire type.

In protective systems of. this type the use of a single protective transformer of the double core type at each of two separate points of an alternating electric current distribution system responsive to the currents in all the conductors thereof for protection against faults to earth and faults between phases in the section between the two points is sometime disadvantageous. This is more especially the case in high tension distribution systems of say above 11000 volts as it is sometimes difficult to design a protective transformer whichcan be sufficiently insulated and at the same time does not exceed the dimensions of the usual cable box.

Considerable trouble with faults has been experienced at the place where the conductors of a. high tension cable are brought from the pothead due to the fact that it is difiicult to provide the necessary insulation. This difiiculty may be largely overcome by properly spacing and insulating the conductors of the cable where they leave the pothead, but with a single protective trans former of the double core type, the spacing between the conductors is somewhat limited and it is desirable to have a greater working range for this spacing. Furthermore the application of a single protective transformer of the double core type to an overhead line is somewhat disadvantageous as it would be necessary to bring the conductors relatively close to each other, thus increasing the difiiculties of insulation.

It is therefore an object of my invention to provide a protective system of the pilot wire type with an arrangement of double core protective transformers for protecting an alternating electric current system against faults to earth and faults between phases which provides a greater working range with respect to the insulation and size of the respective transformers and the dis position of the conductors of the system at the points where the transformers are located.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the single figure of the accompanying drawing, which is a diagrammatic representation of a protective system embodying my invention, lines 1, 2 and 3 represent the conductors of a three-phase alternating electric current system embodying my invention, parts of three sections of the line being shown. At each end of the middle section of the line, there are shown a plurality of cooperating transformers 4, 4, one for each conductor of the line at each of two separate points thereof. Each of these transformers i, i is arranged in series relation with its respective conductor and comprise an inner core 5 and an outer core 6, arranged symmetrically with respect to the related conductor and preferably concentrically arranged as shown. The outer core 6 is preferably a closed core to provide a path of relatively low magnetic reluctance and theinner core 5 is preferably provided with an air gap 7 or equivalent means to provide a path of relatively high magnetic reluctance.

The outer core 6 is provided with a wind ing 8 and the windings 8 of the transformers 4 are connected in parallel as are also the windings 8 of the transformers 4: The resultant electromotive force of each set of parallel connected windings is therefore normally zero. These sets of parallel connected windings are interconnected between thetwo points for opposing electromotive forces by a pilot wire 9 having relays 10 in circuit therewith and a return pilot wire 11. In this manner, the input of electric energy into the section of the line 123 between the points at which the transformers 4, 4 are located is balanced against the output therefrom. The relays 10 may be arranged. to control the opening of circuit breakers in the line 1'23 in a manner well known to the art.

Since the reluctance of the magnetic circuit of each of the windings 8 is relatively low, these windings will be relatively sensitire on faults to earth, while on faults between phases the resultant. electromotive force of each set of windings remain substantially zero. With a fault to earth on any of the conductors 1, 2, 8, each set of parallel connected windings 8 will have a resultant electromotive force which is not zero. These resultant electromotive forces will be alike in value if the fault is not in the section of the line 1, 2, 3 between the points at which the transformers 4t and 4 are located and therefore since the sets of windings 8' are interconnected between these points for opposing electromotive forces, the relays 10 will not be energized since the opposing 'electromotive forces are equal. If, however, the fault is in the section of the line 123 between the points at which the transformers t and 4t are located, the resultant electromotive forces of the two sets of windings 8' are no longer equal and current will flow say from windings 8 of transformers 4 through pilot wire 9 and relays 10 to windings 8 of transformers 4; and back through the pilot wire 11 to the windings 8 of the transformers a. The inner core 5 of each of the transformers 4, r is provided with a winding 12 and the windings 12 of the transformers t are connected in series as are also the windings 12 of the transformers 4E,

' each set of windings being connected in a similar manner normally to produce equal resultant electromotive forces. These sets of series connected windings are interconnected for opposing electromotive forces: by a pilot wire 13 having relays ll in circuit therewith and the return pilot wire 11. In this manner the input of electric energy into the section of the line 12-3 between the points at which the transformers 4t, 4: are located is balanced against the output therefrom. The relays is maybe arranged to control circuit breakers in the line 1-2-3 in a manner well known to the art.

Since the reluctance of the magnetic circult of each of the windings 12 is relatively high, these windings will be relatively insensitive on faults to earth and relatively sensitive on faults between phases. Normally the resultant electro-motive forces of the two sets of series connected windings 12 are equal and since these sets are connected in, opposition no current flows through the relays 12. Upon the occurrence of a fault between phases on the line 123, the resultant electromotive forces of the two sets of windings will change but ifthe fault is not in the section between the points at which the transformers 4, 4c" are connected the resultant electromotive force of each set of windings 12 will be the same and since these sets are connected in opposition no current will flow through the relays 14;. If,

however, the fault between phases is in the section of the line 1'-2-3 between the points at which the transformers 4:, 4: are located, the resultant electromotive forces 7 of the two sets of windings 12 are no longer equal and: current will flow say from winding-s 12 0f the transformers t through pilot wire 13 and relays 1a to the windings 12 of for faults between phases through relays- 14 which may be set relatively insensitive on faults to earth and yet be relatively sensitive on faults between phases.

What I claim as new and desire to secure by Letters Patent of the United States, is, Y

1. Protective means for an alternating electric current system comprising a transformer in series relation with each conductor of the system at each of two separate points thereof, each of said transformers comprising inner and outer cores, and windings on said cores, said windings beingiirterconnected between said points to balance the input of electric energy into the section between said points against the output therefrom, whereby the windings on said outer cores are adapted to yield operating currents on faults to earth in said section and the windings on said inner cores to yield operating currents on faults between phases in said section.

2. Protective means for an alternating current system. comprising a. transformer in series relation with each conductor of the system at each of two separate points thereof, each of said transformers comprising inner and outer cores, and windings on said cores, the windings on the inner cores of the transformers at each point being connected in series and interconnected between said points for opposing electromotive forces and being thereby adapted to yield operating currents on faults between phases in the sect-ion between said points, and the windings on the outer cores of the trans formers at each point being connected in paralled and interconnected between said points for opposing electromotive forcesand being thereby adapted to yield operating currents on faults to earth in the section be tween said points.

3. Protective meansfor a polyphasealternating electric current system comprising plurality of current transformers, one for each phase of the system at each of two separate points thereof, each of said transformers comprising concentric inner and outer cores, and windings on said cores, the windings on the outer cores of the transformers at each of said points being connected in parallel and interconnected between said points for opposing electromotive forces whereby said windings are adapted to yield operating currents on faults to earth in the section between said points and the windings on the inner cores of the transformers at each of said points being connected in series and interconnected between said points for opposing electromotive forces whereby said windings are adapted to yield operating currents on faults between phases in the section between said points.

4. Protective means for a three phase alternating electric current system comprising a protective transformer for each conductor of the system at each of two separate points thereof arranged in series relation with said conductor and comprising inner and outer cores, windings on said cores, the windings on the inner cores of the transformers at each point being connected in series and interconnected between said points for opposing electromotive forces and the windings on the outer coresof the transformers at each point being connected in parallel and interconnected between said points for opposing electromotive forces.

5. In combination with a three phase alternating electric current system, a protective transformer in series relation with each conductor of the system at each of two separate points thereof each of said transformers comprising an outer closed core and an inner core concentric therewith and having relatively high reluctance, and windings on Said cores interconnected between said points to balance the input of electric energy into the section between said points against the output therefrom, the windings on said outer cores being adapted to yield operating currents on faults to earth in said section and the windings on said inner cores to yield operating currents on faults between phases in said section.

6. Protective means for an alternating electric current system comprising a plurality of current transformers at each of two separate points of the system, each of said transformers comprising an outer closed core and a concentric inner core of relatively high reluctance, a conductor within said inner core in series relation with one of the conductors of the system, windings on the inner cores of the transformers at each of said points, said windings being connected in series at each of said points and interconnected between said points for opposing electromotive forces, and windings on the outer cores of the transformers at each of said points, said windings being connected in parallel at each of said points and interbonnected between said points for opposing electromotive forces.

7 Protective means for a polyphase alternatin electric current system comprising a transformer for each phase of the system at each of two separate points thereof, each transformer comprising an outer core and an inner core provided with an air gap, windings on said cores, and a conductor within said cores in series relation with one of the conductors of the system, the windings on the outer cores of the transformers at each of said points being connected normally to yield no current and interconnected between said points for opposing electromotive forces whereby said windings are adapted to yield operating currents on faults to earth in the section between said points and the windings on the inner cores of the trans formers at each of said points being connected in series and interconnected between said points for opposing electromotive forces whereby said windings are adapted to yield operating currents on faults between phases in the section between said points.

In witness whereof, I have hereunto set my hand this 22nd day of December, 1921.

HENRY TRENCH'AM. 

